1. Field of the Invention
The present invention relates to a sensor system, which includes a rotational angle sensor and a torque sensor, and a method for detecting a rotational angle and a torque.
2. Description of Related Art
In electronic steering systems or EPS (electric power steering) systems, a measurement of the torque on the steering wheel is required. The torque or steering moment, which the driver generates on the steering wheel, results in twisting of a torsion bar by an angle proportional to the torque, which is measured by a torque sensor (TSS, torque steering sensor). EPS systems have significant advantages over typical hydraulic-based steering support systems, which is why these are expected to be completely replaced by EPS steering systems in the future.
The measurement of the rotational or steering angle is required, for example, for the ESP (electronic stability program). All vehicle classes are increasingly being equipped with steering angle sensors due to the propagation of the ESP as a fixed component of accident avoidance systems. Steering angle information is also used in other systems, such as PP (park pilot), ACC (adaptive cruise control), 4WD (four-wheel-drive), DDD (driver drowsiness detection), etc. Different requirements are placed on a steering angle measurement depending on the vehicle equipment. A steering angle sensor (LWS) of Robert Bosch GmbH having high resolution and precision is, for example, the LWS5 (class 111 sensor).
In some torque angle sensors (TAS), concepts for measuring the torque based on induction coils, sliding contacts, or magnetic circuits are used. The individual parts of rotational angle and torque sensors are typically based on magnetic principles. In a torque sensor, an index signal is integrated as an additional element, which provides a switching pulse when the steering is in the “drive straight ahead position.” Gear wheels are used for angle recognition in steering angle sensor LWS5 of Robert Bosch GmbH.
A sensor system for detecting a differential angle is described in the published German patent application document DE 10 2005 031 086 A1. The sensor system includes at least one magnetic-field-sensitive sensor element, using which the magnetic field information of a magnetic circuit, which has a magnetic pole wheel connectable to a shaft and ferromagnetic flux rings having teeth, may be analyzed. The teeth run in the radial direction of the shaft for radially picking off the magnetic field information of the magnetic pole wheel.
The published German patent application document DE 195 06 938 A1 describes a method and a device for measuring the angle of a body rotatable by more than 360°. In this case, this rotatable body cooperates with at least two other rotatable gear wheels, whose angular position is ascertained with the aid of two sensors. The angle location of the rotatable body is determined from the angular positions thus ascertained. In order for definite statements to be possible, it is necessary for all three rotatable bodies or gear wheels to have specific predefinable tooth counts. The method and the device may be used to ascertain the steering angle of a motor vehicle, for example.
A system for detecting rotational angles on a rotating component having transmitters and sensors is described in the published German patent application document DE 10 2008 011 448, which detects changes of a physical variable generated by the transmitters as a function of the rotational angle change of the rotating component as signals which may be digitally analyzed. The rotating component has at least one satellite of smaller circumference, which is coupled to its circumference and rotates through its rotation, preferably having an angle sensor. The satellite drives, via an axially coupled hypocycloid gear, a hypocycloid disk or hypocycloid gear wheel which also rotates, whose rotational velocity may be stepped down by the hypocycloid gear in such a way that a revolution speed of the rotating component and the absolute steering angle over multiple revolutions of the steering shaft may be determined therefrom.